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  #51  
Old 6th October 2018
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Quote:
Originally Posted by brucstoudt View Post
nice to go back through sc72's thread again.that was a good one.
I enjoyed reading that.

I wondered how the grooves in the cover and the body got in that specific spot.
They are not very deep. The closeup makes it look bigger.
I can feel it as rough with my fingernail, but it doesn’t grab.
See the groove that has been cut into the larger pad on the left?


I decided to find out why it is in that certain spot on many used pumps.
Sometimes, the small pad to the right is scratched or damaged also but not always.
It happens to be right at the seam between the inner and outer gerotor on both the feed and return sides.
Debris caught between these two gears cannot slide over and fall to the other cavity and out of the pump.



The inner gerotor spins in this same position as it is mounted to the gearshaft.
The outer gerotor spins by way of the gears inside the cover but also in the same position to the inner gear as below in operation.
The gearshaft is off center to the outside gerotors both feed and return.
There are 8 teeth on the inner and 9 on the outer gerotor in each set.
This allows for the cavity between the inner and outer gears for oil transfer.

In theory, no particles of any size should be able to spin around to the small pad due to the pressure generated by the spring washer and the gerotor spacing there.
The side toward the motor is where oil is transferred to and from the pump.
The inner and outer gears come together on the other side (right side).
This spacing relationship doesn't change between the motor side or the outside of the pump due to the offset gearshaft.
Left side of 1st pic below goes toward the motor.

Top in this pic is the motor side.


The spring washer resides between the two plates and is supposed to keep each plate pressured against each gerotor set.
This should keep down cross connection of oil between the feed and return side.
And allow differential oil pressures on each side, I think.


However, when a piece of trash / debris gets into the supply side of the cavity and crunched between the gerotors, it gets carried past the output cavity and spins around to the other side where the inner and outer gears come together.
The small space between the gears won’t change.
So any debris that doesn’t get crunched up here causes the gerotor to jolt and rise / fall toward the spring since there is nowhere to go against the cover or body.
The debris slides and rotates between the gerotor and the aluminum cover or body and rips into the aluminum surface on its way around.
So, the spring can be a blessing or a curse depending on how you look at it.
It helps keep the pump from locking up immediately from debris.
But it also allows for the destruction of the gerotor surfaces.

edit: This is what I see just from the time I spent on it.
If you look at something long enough, you can get tunnel vision though...
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Last edited by Hippysmack; 9th January 2019 at 17:52.. Reason: labeling pics
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  #52  
Old 7th October 2018
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Now, I’m not in any way going to pretend to be an expert on any of this.
I’ve been wrenching most of my life and mostly on my own stuff without asking but just doing.
Approaching mid 50’s, I’m finally asking the why’s.
Some of this also applies to EVO gerotor pumps.
But, someone let me know if I go off the rails.

Also, if the pics get too much, just let me know and I’ll leave them out.
I’m just linking to ones I’ve added to the Sportsterpedia for reference.

I've was thinking about the effects of the scratches in the aluminum cover and pump at the gerotor surfaces.

The 70-78 FSM says
• In a gerotor type pump, oil is transferred from the inlet to the outlet as it is trapped between the rotating inner and outer gerotors.
• During the first 180 degrees of rotation, the cavity between the inner and outer elements gradually increases in size.
Maximum cavity volume is equal to the full volume of the missing tooth.
The gradually enlarging cavity creates a vacuum into which the oil flows out from the inlet.
• During the next 180 degrees of rotation, the size of the cavity decreases forcing oil into the outlet (cavity).

So, pressure is created to the check valve and subsequently to the engine by the closing of the space between the gerotors at the output cavity while it is filled with oil.

I see that as kinda like cupping your hands together and then squishing them flat, which is more of a diaphragm effect.

But neither the supply nor output cavity is ever truly closed off by one gerotor tooth of oil.
At no time is there less than three or more than four gerotor teeth carrying or releasing oil over the output cavity.

So, in theory and plugging up the check valve for this idea, downward pressure created into the cavity where the gears come together will be pushed back out of the same cavity through the gerotors with the wider spacing between the teeth.



This is compensated for by the spring washer pressing the outer plate against the top of the feed gerotor and the flat surface in the cover (that the gerotors turn against) which leaves the pressure nowhere to go but into the check valve.

This keeps the output side cavity pressurized enough to overcome the small spring pressure of the check valve for oil to travel up and into the engine.



That brings me to the scratches in the cover. I’d think there would be some reduced pressure because of them.

Pressure generated to the output cavity can squirt back to the input side through these scratches.


How much pressure loss would depend on the width, depth, length of the scratches and oil viscosity.

To make the pump inoperative or not make pressure (from the scratches alone), they would have to be proportional to the relative volume of all four gerotor reservoirs combined, I think.
Then, the check valve would have to accept less pressure flow than the backpressure from the pump.


So, I'd think the gerotor surface in the cover would have to be eat up pretty bad to make the pump ineffective on a warmed-up engine?

The pump would have less pressure loss with multi-weight or straight 50 or 60 when cold than hot. They'll both flow faster when hot.

Last edited by Hippysmack; 4th December 2018 at 21:43.. Reason: Updated pic
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  #53  
Old 8th October 2018
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Cory, do you have a set of gerotors without the chamfer?
I'd like to stack your dims up to mine, especially thickness.
I'm having trouble getting this pump back together without it binding up as before.

I originally thought it was a bent gearshaft. But, I took it back apart and tested the shaft to run true.
It spins fine until I add the cover. I took the gerotors out, shoved the gearshaft into the assembly and it spins fine.
Add the gerotors and it binds up.

Here are the dims for the chamfered gerotors I have.
Feed:




Return:


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  #54  
Old 8th October 2018
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I've got the gerotors without chamfer. I'll measure tomorrow.

In my experience with these pumps, when you put the cover on, the spring that presses against the outer plate created a decent resistance. When I just put my pump together for my 78 a few weeks ago, I used a new spring. The resistance was even more than with the older one. But it is consistent .

One thing that can very easily bind up these pumps is the outer plate and the roll pin in the pump body. All it takes is a little bit of rotation of the gear shaft when puting the cover on to misalign the outer plate to the roll pin. If it's off then the outer plate hits the roll pin leaves it cockeyed. I've got pictures of outer plate where this happened.

Installing the pump on the motor is about the most stressful part of the entire build of a motor too me. You have to be so careful.
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  #55  
Old 8th October 2018
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It must have a lot more resistance than the later pumps then.
It's akin to turning a manual can opener on a can of beans.

I'll try again more carefully.

The bushings are out of spec 1/2 to 1 thou also. Should be .0005" clearance max.
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  #56  
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Try without the spring to see how much difference it makes.
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  #57  
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Just tried it.
Without the spring, there is less resistance than the 98 pump and it turns smooth.

I had to use two fingers to have a chance at turning this pump with the gears in.
The later pumps will turn with pressured applied by 1 finger in a turning motion.

Is there a home grown way to measure the resistance?

Maybe a fish scale and string?
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Gerotor square cut dims

Feed-0.180 thick, 1.494 diameter (NOS part I have is the same)
Return-0.498 thick, 1.494 diameter (no NOS to compare to)

I find same dimensions from chamfer to square cut gerotors
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  #59  
Old 9th October 2018
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Thanks for the dims.

That confirms that it is the spring washer that induces the resistance on the gear to turn.
I took the spring washer out, assembled the gerotors and got no resistance and it turns smooth.

Seems like the resistance would create extra drag on the pinion shaft.
It may not be a mechanical issue due to the splines holding the oil pump gear on the pinion shaft.
I'd think the oil pump gear would break before the pinion shaft would let go of it.

91 and up pumps have less resistance on the turning of the pump gearshaft.

But, they changed to a smooth pinion shaft with a woodruff key to hold the oil pump and pinion gears and took the spring washer out of the pump.
Maybe the resistance was too much for the woodruff key?

I wanted to compare the mounting surfaces between this pump (for posterity a 79) and the 91 and up style pumps.
I put the 98 style gasket on the 79 pump and it fit like it's supposed to.
It's snug around the gearshaft housing and all the bolt holes match up.


I cut a 1-1/2" hole in an aluminum plate and tapped 4 holes to mount the pump.


Used a sharpie to outline it.


Then mounted a 98 oil pump to the plate and outlined it in pencil.


This shows the mounted differences in them.


I measured .034" milled down on the 79 pump.
The later style pump bodies got a little more narrow although still overlapping the milled area of the 79 slightly.

The bolt mounting holes in the 79 pump are slightly wider giving a little more slop when I mounted it to the plate.
The 98 had less slop due to the mounting holes having less clearance around the bolts but bolted up fine.

Question:
How does the oil get to the filter?
The FSM says it runs from the pump into the gearcase cover and details from there back to the tank without mention of the filtering process.. unless I missed something.

edit: I moved the pics to the pedia and added a red circle on the last pic to show where I believe the hole in the engine case should line up.

Last edited by Hippysmack; 11th December 2018 at 20:50.. Reason: Changed links to pics.
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Quote:
Originally Posted by Hippysmack View Post
Thanks for the dims.

That confirms that it is the spring washer that induces the resistance on the gear to turn.
I took the spring washer out, assembled the gerotors and got no resistance and it turns smooth.

this has been my experience with all of these pumps I have handled. Like I said before, I used a NOS spring this last time and it's is quite hard to turn the pump by hand. Hard enough I took it back apart twice to double check.

Seems like the resistance would create extra drag on the pinion shaft.
It may not be a mechanical issue due to the splines holding the oil pump gear on the pinion shaft.
I'd think the oil pump gear would break before the pinion shaft would let go of it.

when was in taking my pump this last time I was observing something that I never noticed before as far as what I see to be unsettling. When the pinion drive gear turns the pump, it lifts the pump drive gear up. What stops it? The retaining ring. Notice how when pump is assembled, the gear shaft has up and down play. It is what ever slack there is between the retaining ring, return gerotors and the pump body. So if that retain ring ever let go of its grove in the drive shaft, the drive shaft could to lift up untill it colides with the #2 cam. This would be catastrophic damage. I've never heard of it happening, but somewhat unsettling knowing how critical that retaining ring is and how there is hardly anything to it.

91 and up pumps have less resistance on the turning of the pump gearshaft.

But, they changed to a smooth pinion shaft with a woodruff key to hold the oil pump and pinion gears and took the spring washer out of the pump.
Maybe the resistance was too much for the woodruff key?



Question:
How does the oil get to the filter?
The FSM says it runs from the pump into the gearcase cover and details from there back to the tank without mention of the filtering process.. unless I missed something.
I don't know about later than 78, but the XLCH model did not have a filter at all, the XLH model had an in yank filter. At the end of the return, the oil dumps into the filter as it goes in the tank
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